Effect of support material creep on the delamination failure of air plasma sprayed thermal barrier coatings

The effect of support material creep on failure of ceramic thermal barrier coating (TBC) was studied. A simplified cylindrical model TBC-system was used: Instead of Ni-superalloy and bond coat (BC) the substrates consisted of a Fe–Cr–Al–Y-alloy with BC-like chemical composition, namely Fecralloy with low creep strength and oxide dispersoid strengthened PM2000 Fe–Cr–Al–Y samples. After sandblasting the substrates surface, yttria stabilized zirconia thermal barrier coatings were applied by air plasma spraying. Slices were extracted from the cylindrical specimens and the lateral slice-surfaces were polished. Then they were thermally cycled to assess the effect of support material creep on delamination induced TBC failure. The damage evolution was examined at the lateral slice cross-sectional surface after different numbers of thermal cycles. The study shows a significant delay and deceleration of delamination crack growth for the low creep strength Fecralloy, in contrast to observations made for the high creep strength substrate material. The experimental results indicate that stresses which promote delamination failure are partially relaxed by creep deformation in the near interface regions, which appear to be more pronounced for support materials with low creep strength.